1. Field of the Invention
The invention relates to the field of valves for use with water meters or the like, and more particularly to a throttle valve for use with a water meter to prevent excessive flow of water through the meter.
2. Description of the Prior Art
Water meters and flow regulating valves come in a wide variety of sizes and designs.
One type of water metering apparatus is a so-called "compound-type fire service" meter. Fire service meters are designed to be connected in a supply line leading from a water main to the structure to be protected.
Water supply line sizes can range from 4 inches up to 10 inches or greater in diameter. The supply line is used to supply potable water for consumption by the occupants of the structure. The supply line is also frequently connected to a water sprinkler system contained within the structure or to pressurized standpipes or hydrants located in or about the structure for use by a fire department in the event a fire occurs on the premises.
A fire service meter is often used to measure the amount of water being supplied to a business establishment, apartment building, office building or the like. The range of measurement for such devices under normal conditions would be from less than 1 gallon per minute to about 1000 gallons per minute. However, under extraordinary conditions, e.g. when there is a fire and a sprinkler system or other fire fighting apparatus are connected to the water main, flow rates of over 5,000 gallons per minute may be necessary.
Compound-type fire service meters are generally characterized by having two flow measuring elements connected in parallel, with a common inlet and a commonoutlet disposed in the water supply line. A first measuring element is comprised of a conventional positive displacement water meter, such as the Schlumberger Neptune.RTM. T-10 water meter. This type of meter is designed to have high accuracy in measuring relatively low flow rates (e.g. 3/4 of a gallon per minute flow up to 55 gallons per minute, depending upon the meter size). The other measuring element is generally a turbine type flowmeter. Turbine flow meters generally have poor accuracy at low flow rates but are capable of good accuracy at much higher flow rates than a positive displacement type water meter. For example, a turbine meter, depending upon its diameter and design, may measure flow rates accurately of 60 gallons per minute up to more than 5,000 gallons per minute.
The positive displacement meter and the turbine meter work together so that the positive displacement meter measures water flow accurately through the supply line at low flow rates and the turbine meter measures water consumption in cases where intermediate to high flow rates occur, e.g. when water is being drawn through the supply line due to large water demand such as might occur when a sprinkler system is activated or where fire fighting apparatus is connected to the supply line to draw water in high volumes.
One such type of conventional fire service meter is the Schlumberger NEPTUNE.RTM. PROTECTUS.RTM. III. In addition to a positive displacement meter and a turbine meter, this type of fire service meter includes a pressure sensitive check valve, comprised of a spring-loaded diaphragm placed in the main supply line adjacent the turbine meter. This valve is designed to open when a certain flow rate is reached or exceeded. Thus, in low water demand situations, the valve remains closed, causing water in the supply line to bypass the turbine meter and flow only through the positive displacement meter section of the fire service meter. The positive displacement meter measures water flow accurately at low flow rates.
When the flow rate exceeds a certain predetermined amount, the check valve in the main supply line begins to open, allowing water to flow through the main supply line and through the turbine flow meter. When the check valve is fully open, most of the water flows through the main supply line and through the turbine meter with the positive displacement meter still running at or above the flow rate at which the valve started to open.
At this point, the turbine meter is operating well within its normal operating measurement range. However, the positive displacement meter is now running at or above its normal maximum continuous design flow rate. If this condition continues for extended periods, it can cause excessive wear to the positive displacement flow meter resulting in possible damage to the meter.
Another drawback to the foregoing arrangement is that during the transition from the low flow range to the high flow range, i.e. during the period in which the check valve is beginning to open but not yet fully opened, the turbine flow meter is not operating within its most accurate range. The positive displacement meter is operating at or near its maximum continuous design flow rate, while the turbine meter is generally operating at its lowest and least accurate flow range.
It would therefore be desirable to have a compound-type fire service meter in which the transition range from low flow to high flow was made as short as possible. It would also desirable if a compound-type fire service meter of the type described above was designed to ensure rapid opening of the check valve at a predetermined flow rate to thus minimize the transitional flow range. It would be a further desirable feature for a compound-type fire service meter to have some means for protecting the positive displacement meter from being subject to higher than desirable flow rates to prevent wear or damage to the positive displacement meter, if it operates at intermediate to high flow rates for extended periods.